Engine fueling control for catalyst desulfurization

Abstract

A method is described for controlling decontamination of an emission control device. Temperature of the emission control device is maintained at a desired temperature by operating some cylinders of the engine lean and others rich. These lean and rich mixtures react exothermically in the exhaust gas and in the emission control device to generate heat. Efficient contaminant removal is obtained by oscillating the mixture air-fuel ratio about stoichiometry. This oscillation is provided by adjusting the fuel provided to the rich cylinders, or by adjusting the air provided to the lean cylinders, thereby minimizing any torque disturbance corresponding to the oscillations in exhaust air-fuel ratio.

What is claimed is:  
     
       1. A method for controlling an engine having a first and second group of cylinders, both of which are coupled to an emission control device, the method comprising: 
       operating the first group on average at a first rich air-fuel ratio;  
       operating the second group at a second air-fuel ratio; and  
       adjusting said second air-fuel ratio by controlling air entering the second group to cause a mixture air-fuel ratio of a mixture of gasses from the first and second group to oscillate around a predetermined air-fuel ratio based on a sensor coupled downstream of the emission control device.  
     
     
       2. The method of  claim 1  wherein said second air-fuel ratio is lean of stoichiometry. 
     
     
       3. A system, comprising: 
       an engine having a first group of cylinders and a second group of cylinders;  
       an emission control device coupled to the first group and to the second group;  
       a first actuator coupled to the first group for adjusting at least one of an intake or exhaust valve of the first group of cylinders;  
       a second actuator coupled to the second group for adjusting at least one of an intake or exhaust valve of the second group of cylinders; and  
       a controller for operating said first group at a first rich air-fuel ratio, operating said second group at a second lean air-fuel ratio by adding additional air compared with said first group, with said adding air obtained by adjusting said second actuator to a position different than said first actuator, and modifying said first rich air-fuel ratio by adjusting fuel injected into said first cylinder group to cause a mixture air-fuel ratio of a mixture of gasses from the first and second group to oscillate around a predetermined air-fuel ratio.  
     
     
       4. The method recited in  claim 3 , wherein said first and second actuators are variable cam timing systems. 
     
     
       5. The method recited in  claim 3 , wherein said first and second actuators are variable valve lift systems. 
     
     
       6. The method recited in  claim 3 , further comprising a sensor coupled downstream of said emission control device. 
     
     
       7. A method for controlling an engine having a first and second group of cylinders, both of which are coupled to an emission control device, the method comprising: 
       operating the first group on average at a first lean air-fuel ratio;  
       operating the second group at a second rich air-fuel ratio wherein said second air-fuel ratio is adjusted between a first rich air-fuel ratio and a second, less rich, rich air-fuel ratio; and  
       adjusting said second air-fuel ratio between said first rich and said second rich air-fuel ratios based on an operating condition by controlling at least fuel injected into the second group; said adjusting causing a mixture air-fuel ratio of a mixture of gasses from the first and second cylinder groups to oscillate between a lean air-fuel ratio and a rich air-fuel ratio.